Acrylonitrile copolymers capable of forming hydrogels containing at least 90% by weight of water at room temperature are well known in the art. Preferably, the total number of nitrile groups ##STR1## in such copolymers is between 5 and 75 percent (more preferably between 10 and 50 percent) of all substituent groups present, and at least 1/5 of such nitrile groups (preferably at least 1/2 ) are arranged in sequences containing at least 5 adjacent nitrile groups; they may be considered either graft or block copolymers, preferably the latter.
One group of such acrylonitrile-based hydrogels is linear polymers having a hydrocarbon backbone to which are bonded nitrile groups along with other substituent groups such as carboxyl, carboxylate salt, carboxylic ester, and amide and imide groups. They may or may not be covalently cross-linked. For the most part such copolymers are made by partial hydrolysis of polyacrylonitrile (PAN) under appropriate conditions; the hydrolysis can be catalyzed by either acid or base. They are described, for example, in Stoy U.S. Pat. No. 4,107,121, which is incorporated herein by reference.
Another group of such acrylonitrile-based hydrogels is polysaccharides, e.g., starch, grafted with polyacrylonitrile segments (SPAN), which are then hydrolyzed with base to acrylic acid or acrylamide segments to form the hydrogels. Under certain controlled hydrolysis conditions, however, the hydrolyzed copolymer contains residual nitrile groups in sequences of 5 or more.
The acrylonitrile copolymer emulsifying and dispersing agents of the present invention are those acrylonitrile copolymers which are capable of forming hydrogels containing at least 90% by weight of water at room temperature, i.e. hydrogels which retain their form and shape without liquid flow when allowed to stand at room temperature. Such copolymers are, as a rule, not crosslinked by covalent bonds. The three-dimensional network in such hydrogels is formed by interactions between the nitrile group ##STR2## sequences which form crystalline clusters. The clusters are crystalline domains whose structure resembles closely that of PAN itself (for instance, the essential features typical for PAN can be detected in X-ray diffraction patterns of such hydrogels). The hydrogels can also be formed by acrylonitrile copolymers crosslinked covalently to supplement the physical network of the type indicated above, although the latter is dominant with respect to the important physical properties.
The emulsions and dispersions of the present invention contain an aqueous polar phase and a water-insoluble nonpolar phase. The aqueous phase may contain in addition to water various water-soluble polar materials such as alcohol, glycols, acids and/or salts thereof, while the non-polar phase may contain a variety of water-insoluble solids or water-insoluble non-polar liquids with or without water-insoluble solids dissolved therein. Examples of important emulsions and dispersions which can be made in accordance with the present invention and their uses are milk and other food products; food substitutes and additives; latices, both synthetic and natural, e.g. latex paints and adhesives; creams, lotions, and ointments in cosmetics and health care; cooling and lubricating emulsions, hydraulic fluids; emulsion polymerization medium for numerous important monomers; liquid membrane systems, drug delivery systems, implantable tissue augmentation and many others. Recently, one special group of emulsions (liposomes) is being developed for targeted and controlled drug delivery.